Process of manufacturing aluminum-lead bearing material

ABSTRACT

A process for the manufacture of aluminum-lead materials with lead proportions from 3 to 26 percent by weight, especially for use as journal or bearing materials wherein atomized overheated molten particles of the material are very rapidly solidified to form granules. A mass of the granules may be mechanically worked to produce a semi-finished article.

"United States Patent 1191 Betz et al.

[4 1 Sept. 16, 1975 PROCESS OF MANUFACTURING ALUlVlINUM-LEAD BEARING MATERIAL [76] inventors: Hans Betz, Dantestrasse 5,

62-Wiesbaden; Dietrich Merz, Fischbacher Str. 24, 6233-Kelkheim; Heinrich Winter, Kurt-Schumacher, Str. 4, 6236 Eschbom; Hans Ahlborn, Hausdeich 141 2053 Hamburg, all of Germany [22] Filed: Jan. 23, 1974 [21] Appl. No.: 435,868

[52] US. Cl. 29/149.5 S; 29/149.5 PM; 29/4205; 29/5277; 29/DIG. 39; 164/46 [51] Int. Cl. B21D 53/10; B22D 23/00 [58] Field of Search 264/8, 13, 14; 164/46; 29/4205, 527.7, DIG. 39,1495 PM, 149.5 S; 75/138 [56] References Cited UNITED STATES PATENTS 3,138,851 6/1964 Radkc et al 29/4205 UX 3,241,948 3 1966 Claiborne et al. 264/8 x 3,329,746 7/1967 Joyce et a1 264 8 3,410,331 11/1968 Miller et a1. 164/51 3,432,293 3/1969 Michael et 31.... 75 138 3,562,884 2/1971 Webbere 29/1495 s 3,689,987 9 1972 Teague 164 46 x 3,797,084 3 1974 Fedor et al..... 29/1495 PM 3,827,882 8/1974 Lloyd et 31.... 75/138 3,833,983 9/1974v :Baker, et a]. 29/1495 8 Primary ExaminerRichar d J. Herbst Assistant Examiner-D. C. Reiley, Ill

Attorney, Agent, or Firm-Strauch, Nolan, Neale, Nies & Kurz [57] ABSTRACT A process for the manufacture of aluminum-lead materials with lead proportions from 3 to 26 percent by weight, especially for use as journal or bearing materials wherein atomized overheated molten particles of the material are very rapidly solidified to form granules. A mass of the granules may be mechanically worked to produce a semi-finished article.

7 Claims, 4 Drawing Figures PA'nirmau SEP 1 s @915 3,905 085 SHEET 1 [1f 2 (P020140 so 90 9e 99 Wt Pb Atom-%Pb Fig. 7

0 2 5 0 0000 0 OOOOOOOQQO/I PATENTEU sEP 1 6 ms f SHEET 2 2 Fig.3

PROCESS or MANUFACTURING ALUMINUM-LEAD BEARING MATERIAL BACKGROUND OF THE INVENTION Bearing materials based on aluminum containing high proportions of tin are useful in practice. Similar to v throughout the aluminum matrix, then'one might expect outstanding frictionally low gliding properties. Also, such materials would be appreciably more economical than the previously used aluminum-tin alloys. However, no appropriate process was previously known for manufacturing on an industrial'scale aluminum-lead alloys suitable as bearing materials.

It is true that the proposal already was advanced to separately melt aluminum and lead and to cast both melts together in free fall and to let them drop upon a cooled surface (German Offenlegungsschrift No. 1,533,254). However, as shown in practice, one may only achieve relative coarse distribution of the lead through the aluminum structure. Because of the known miscibility gap of aluminum and lead in the liquid state, the separate melts brought together in this process will have to be heated much beyond their melting points in order to mix at all when meeting. This fact increases the technical difficulties, especially with respect of the high affinity of aluminum for the most varied other elements, especially oxygen, which occurs at temperatures above the melting point. Therefore this process so far could not be carried in industrial practice.

Now a proposal also was advanced tothe effect that 7 an aluminum-lead melt first be intensively mixed and then be cooled in controlled manner, and that it be subjected during cooling, especially when passing through the zone of the miscibility gap, to external forces, for

instance gravitational or centrifugal ones (US. Pat. No. 3,410,331). Such a procedure is extraordinarily difficult and foremost fails to achieve an even distribution,

rather it leads to precipitation which can only be controlled by the external forces during the controlled cooling, but not eliminated.

Furthermore the suggestion already has been made with respect to manufacturing aluminum-lead alloys.

that the aluminum and lead melts be separately sprayed upon a steel plate in a nitrogen atmosphere (French Pat. No. 2,095,384). The spraying occurs by atomizing with nitrogen. Themelts are divided into extremely fine droplets on account of the gas flow and are cooled so rapidly as to be nearly solidified when impinging. upon centrifugally deposited by means of this process. They are either wholly or largely solidified already before impinging. Therefore the incorporation of lead particles of the size of microns in an aluminum matrix may not .be achie'ved in this manner. Furthermore, highly pure or inert gases'are'required as protective atmospheres. and drive means. This however will eliminate the eco-" nomic advantage of lead-with respect to tin.

SUMMARY )F THE INVENTION On the other hand, the invention addresses the task of' providing a process for the manufacture of aluminum-lead alloys with lead proportions of 3-26 percent by weight, especially for use in bearing materials, which may be carried out without any difficulties on an industrial scale and which will allow fine and even distribui tion of the lead precipitates throughout the aluminum matrix. Further, the economic advantage of lead with respect to tin shall be maintained. This problem is solved by the invention in that the melt of the alloy constituents is raised to a temperature I above the miscibility gap and is divided into small'melt droplets by evacuation and centrifugation means' known per se, said droplets being converted into granule form by very rapid solidification.

The invention is based on the insight and discovery that obtaining an aluminum-lead alloy .with' fine and even distribution of the lead throughout the aluminum matrix requires more than mere exclusion of gravitational precipitation. All previously known experiments and proposals for obtaining aluminum-lead alloys by cooling the alloy melt failed on account of neglecting additional considerations beyond mere elimination of gravity precipitation. The invention however recognizes the very rapid occurrence of coagulation of the molten lead within the molten aluminum in the form of Ostwald-aging in view of the very high difiusion rate of molten lead and aluminum within the miscibility gap,

said aging being independent of mechanical influences or of forces. Only the very rapid solidification to be carried out in accordance with the invention will allow to freeze the melt so rapidly that precipitation and coagulation will be incapable of causing formation of coarse lead particles.

A process known per se for dividing the-melt into small melt droplets and for the very rapid solidification of latter into granule form (see German Auslegeschrift No. 1,285,098; Ofi'enlegungsschrift No. 1,923,658) will be used in the process of'the invention for the manufacture of other aluminum alloys. When'making use of this known method, as regards now the manufacture of aluminum-lead alloys, there will be the additional difi'iculty with regard to previously known applications that the common melt of the alloy constituents must be raised to a'temperature beyond the miscibility gap. Surprisingly, it was found that despite the very high temperatures occurring in the melt, the granule particles being obtained will be free from any significant oxidation, furthermore that no hydrogen embrittlement occurred even when casting off in centrifugal manner the melt droplets at those high temperatures into the ordinary atmosphere containing water vapor, provided such embrittlement was prevented at the melt surface.

Even more and totally surprising, it was found that in plates or may be extruded into semi-finished products. 7

In another embodiment of the invention, the melt drops in free flight are very rapidly solidified into elongated-round shaped granules. Said granule, which was obtained in air, has a metallically shiny surface and may be most easily rolled directly into plates or sheets or may be compacted into extrusion billets and be subsequently extruded. Because of the relatively low ratio of surface to volume of the particles and becauseof the surprisingly minute oxide skin, the proportion of A1 will not interfere. If one attempted forming appreciably smaller melt droplets by atomizing, then the appreciably larger particle surface to volume ratio would also lead to a considerably higher and interfering proportion of A1 0 flakes so obtained are characterized by extremely finely and evenly distributed lead precipitates in the aluminum matrix. Even when operating in humid air, the surface quality will be outstanding. The flake-like granule may easily be rolled directly into sheets or plates or be compacted and extruded.

Following rolling or extrusion, heat treatment may follow either embodiment and one may obtain in such manner a certain coarsening of the extremely fine lead precipitates in order to set optimum sliding properties of the bearing materials.

It is of special advantage within the scope of the invention that a protective salt cover the hightemperature melt in order to avoid lead losses due to evaporation and in order to prevent hydrogen embrittlement. They may be done at once within the scope of the invention, because the siphon already proposed for implementing the process known per se (German Auslegeschrift No. 1,285,098 or Offenlegungsschrift Nos. 1,923,658 and 2,049,458) may be easily equipped with a sufficiently long suction tube passing through the protective salt layer and sucking the melt from the lower ranges.

The invention achieves an extremely even distribution of very fine lead precipitates throughout the aluminum matrix on account of ensuring the necessary high cooling rates of the high temperature aluminum-lead melt, whereas, as regards the known processes and especially those relating to the castingrolling process (German Offenlegungsschrift Nos. 1,533,254 and 1,913,168), cooling rates of the order of magnitude of l0 C/sec, and as regards atomizing the melt, about C/sec, can be achieved, compared with orders of magnitude of l0C/sec for the process of the invention, such rates being used.

The drawing illustrates the invention.

FIG. 1 shows a temperature-mixing diagram for aluminum and lead;

FIG. 2 is a pictorial representation of an embodiment of the invention;

FIG. 3 is a pictorial representation of a second embodimentof the process of the invention, in side view; and

FIG. 4 is a pictorial representation of the embodiment of the process of FIG. 3 in top view.

DESCRIPTION As shown by FIG. 1, aluminum will be solid up to the temperature of aluminum-side eutectic mixture, i.e.,

658.5 weight-percent of lead content, aluminum and lead will be present in two separate liquid phases and as far as the dissociation curve shown in FIG. 1 by the broken line at the upper diagram edge. The dissociation curve is shown in FIG. 1 in dashed lines above 1,000 for the aluminum side and above l,100 for the lead side, on account of its precise scientific determination as yet being lacking. The alloy is miscible above the dissociation curve and therefore represents a genuine mixture of aluminum and lead atoms.

In conformity with the invention, the state of the alloy melt in FIG. 1 above the dissociation curve should be frozen as much as possible. The larger the temperature interval that is being traversed, and wherein aluminum and lead will be present in separate liquid phases, and the slower the transition through this interval, the larger, that is, the coarser, the precipitated lead particles that are sealed in the aluminum matrix, in view of the diffusion processes that will take place.

As further shown by FIG. l, the temperature at which aluminum and lead will become miscible will strongly increase with increasing lead content along the aluminum-side branch of the dissociation curve. This means that the temperature interval which is to be traversed when freezing the mixing state will also increase appreciably with increasing lead content. Furthermore, the affinity of aluminum for other elements, especially oxygen, hydrogen and the likes, will naturally increase appreciably with increasing temperature.

FIG. 2 shows in schematic form an embodiment of the invention. A centrifugal lifter 2 is immersed from the top into an aluminum-lead melt 1 in the genuine alloying or mixing state, the lifter being made to rotate rapidly by motor 3. As shown, melt 1 is covered by a protective layer 4 consisting of molten salts. Suction lifter 2 by means of its analoguous shank passes through this protective layer 4 into melt 1 and casts off the evacuated melt from its upper part as melt droplets 5 in a circular path symmetrical to its rotational axis, approximately obliquely upwards and radially outwards, as indicated by the paths shown in FIG. 2. Melt droplets 5 will very rapidly cool during their free flight, typically at an average'rate of up to l0 C/sec. Melt droplets 5 will solidify into elongated and round granule particles which, as shown, will be collected in peripheral gutters 6 and will be drained off for further processing.

The example of FIG. 3 and 4 is based on the same design in equipment, though with the difference of there being peripherally mounted cooling surfaces 7 in lieu of the collecting and draining gutters of FIG. 1. Melt droplets 5 will impinge upon these cooling surfaces which are oblique to the flight path and therefore will be very rapidly cooled and thus they will form like flakes or flocks along the cooling surfaces, resulting in a flaking granule 8, which is also collected and removed for further processing. The cooling rates so achieved are higher than for the case of FIG. 1, and

may reach 10 C/sec. As shown in FIG. 4 by the dashed fine precipitate evenly distributed in the aluminum matrix, said process comprising the steps of: melting together aluminum and lead in the desired proportions in said range; heating said melt to a mixing temperature above the miscibility gap of aluminum and lead; covering said overheated melt by a protective layer to prevent lead losses due to evaporation and prevent hydrogen embrittlement; extracting said overheated melt from melt regions below said protection layer and directly centrifugally casting-off said melt to produce droplets; and solidifying the so-produced melt droplets into granules very rapidly so as to substantially freeze miscibility gap.

2. A process as defined in claim 1, characterized in that the melt droplets are brought to very rapid solidification during their free flight into the form of elongatedcircular granules.

3. A process as defined in claim 1, characterized in that the melt droplets are made to impinge upon cooled surfaces on which they spread into thin, flaky granules and where they very rapidly solidify.

4. A process as defined in claim 1, characterized in that the melt droplets are laterally cast off in rotational symmetry with respect to a vertical axis.

5. A process as defined in claim 1, characterized in that the granules are directly rolled into sheets or plates or are compacted and extruded to semi-finished prod- UCtS.

6. A process as defined in claim 1, characterized in that said protective layer is a salt.

7. A process as defined in claim 1, wherein the overheated melt is drawn from beneath the protective layer by suction. 

1. A PROCESS FOR THE MANUFACTURE OF ALUMINUM-LEAD MATERIALS HAVING IN THE RANGE OF ABOUT 3-26 PERCENT BY WEIGHT OF LEAD WHEREIN THE LEAD EXISTS IN THE FORM OF A FINE PRECIPITATE EVENLY DESTRIBUTED IN THE ALUMINUM MATRIX, SAID PROCESS COMPRISING THE STEPS OF: MELTING TOGETHER ALUMINUM AND LEAD IN THE DESIRED PROPORTIONS IN SAID RANGE, HEATING SAID MELT TO A MIXING TEMPERATURE ABOVE THE MISCIBILITY GAP OF ALUMINUM AND LEAD, COVERING SAID OVERHEATED MELT BY A PROTECTIVE LAYER TO PREVENT LEAD LOSES DUE TO EVAPORATION AND PREVENT HYDROGEN EMBRITTLEMENT, EXTRACTING SAID OVEHEATED MELT FROM MELT REGIONS BELOW SAID PROTECTION LAYER AND DIRECTLY CENTRIFUGALLY CASTINGOFF SAID MELT TO PRODUCE DROPLETS, AND SOLIDIFYING TE SO-PRODUCED MELT DROPLETS INTO GRANULES VERY RAPIDLY SO AS TO SUBSTANTIALLY FREEZE THE STATE OF THE OVERHETED MELT PRESENT ABOVE THE SAID MISCIBILITY GAP.
 2. A process as defined in claim 1, characterized in that the melt droplets are brought to very rapid solidification during their free flight into the form of elongatedcircular granules.
 3. A process as defined in claim 1, characterized in that the melt droplets are made to impinge upon cooled surfaces on which they spread into thin, flaky granules and where they very rapidly solidify.
 4. A process as defined in claim 1, characterized in that the melt droplets are laterally cast off in rotational symmetry with respect to a vertical axis.
 5. A process as defined in claim 1, characterized in that the granules are directly rolled into sheets or plates or are compacted and extruded to semi-finished products.
 6. A process as defined in claim 1, characterized in that said protective layer is a salt.
 7. A process as defined in claim 1, wherein the overheated melt is drawn from beneath the protective layer by suction. 